The encapsulation problem of the LAT heavy trays Gamma-ray Large Area Space Telescope The encapsulation problem of the LAT heavy trays Alessandro Brez INFN - Pisa Brez@pi.infn.it

The tray encapsulation DAM Nusil 1142 Fill Nusil 2502 ladder TMCM

The problem Lateral shift On axis shift On all the heavy trays, on both sides, we had bonding failures after thermo cycling. Cause: adhesion failure of the FILL material from the ladder surface (CTE) with subsequent induced over stress on wires

Possible solutions We had no failures (not a single missing connection) in the MID trays, even after 18 thermo cycles (+50,-30oC) Something very special with heavy trays. There is no time to model the problem or to find and test a new fill material. The only practical solution: NO ENCAPSULATION The free wires are much more adaptive to CTE induced movements (loop).

Qualification program From EM trays: Some EM trays have no encapsulation but Most of the EM ladders are from dummy wafers The pitch adapters of the EM TMCMs are different from flight units Several bonding wires have been damaged during the tower thermo-vacuum assembly (thermo couples placed over the trays) These trays have been mounted and dismounted many times There are layers with a complete series of good bondings: They survived to the tower vibe tests They could be tested again in Centrotecnica (is it significant? , they survived to 2 previous tests)

Thermo or thermo vacuum test In principle we can perform a leakage current test In climatic chamber In thermo-vacuum chamber test